Patent Document 1, for example, discloses, as an apparatus that is installed in a vehicle in order to reduce vibration occurring in the vehicle, a drive system rotation variation reduction apparatus that reduces rotation variation in a drive system including an internal combustion engine, a transmission shaft that transmits an output torque of the internal combustion engine to a drive wheel of the vehicle, and a transmission provided on the transmission shaft. The drive system rotation variation reduction apparatus includes varying means for allowing an inertia of the transmission shaft to vary, and control means for controlling the varying means. In the drive system rotation variation reduction apparatus, a damper that absorbs variation in the output torque is provided on the transmission shaft further toward the internal combustion engine side than the transmission, and the varying means allow the inertia of the transmission shaft to vary on the transmission side of the damper. By increasing the inertia of the transmission shaft on the transmission side of the damper in this manner, the drive system rotation variation reduction apparatus can increase the inertia of the transmission shaft while suppressing a reduction in a mode frequency having a primary eigenvalue when the drive system is in a torsional vibration mode. As a result, the drive system rotation variation reduction apparatus can reduce rotation variation in the drive system while suppressing a reduction in vehicle responsiveness.    Patent Document 1: Japanese Patent Application Publication No. 2010-001905